5

Probably:
You wear sunglasses to block out bright sunlight and this is more likely in a convertible with the top down. They might also help keep stuff from blowing into your eyes. By all means if they help you, wear them.
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6

Not at all:
The only real danger is not being able to see what is around you. This is similar to the old wive's tale that reading in dim light is harmful to the eyes. As long as you can see well enough to get by, sunglass wear is not dangerous.
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7

Uv light:
Uv light can be uncomfortable and harmful for the eyes. Almost all sunglasses are made for filtration out of this type of light. Glass is especially good for this., your optician can made recommendations if this is a critical need.
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8

No:
While wearing sunglasses on sunny days to protect your eyes is an excellent idea and will protect your eyes from uv rays, it will not actually "improve" your night vision. Protecting your eyes on sunny days may help with adapting to low light situations, but after 15-30 minutes you vision will have adapted sunglasses or not. Over the long term, not wearing sunglasses can cause some eye damage.
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9

Light input:
Wearing the sunglasses in creases the pupillary size and can alter the focus a little due to this fact. Contacts can provide excellent correction and there can be a slight improvement or decrease with the sunglasses. Not a big effect and not harmful.
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